Limites définies au [RSVP-TE] pour le soutien de l'établissement d'APS
Tunnels via RSVP-TE are also applicable to the establishment of LSP
Tunnels supporting DS-TE. For instance, only unicast LSPs are
supported, and multicast LSPs are for further study.

This new CLASSTYPE object is optional with respect to RSVP so that
general RSVP implementations not concerned with MPLS LSP setup do not
have to support this object.

To establish an LSP tunnel with RSVP, the sender LSR creates a Path
message with a session type of LSP_Tunnel_IPv4 and with a

LABEL_REQUEST object as per [RSVP-TE]. The sender LSR may also
include the DIFFSERV object as per [DIFF-MPLS].

If the LSP is associated with Class-Type 0, the sender LSR MUST NOT
include the CLASSTYPE object in the Path message. This allows
backward compatibility with non-DSTE-configured or non-DSTE-capable
LSRs as discussed below in Section 10 and Appendix C.

If the LSP is associated with Class-Type N (1 <= N <=7), the sender
LSR MUST include the CLASSTYPE object in the Path message with the
Class-Type (CT) field set to N.

If a Path message contains multiple CLASSTYPE objects, only the first
one is meaningful; subsequent CLASSTYPE object(s) MUST be ignored and
MUST NOT be forwarded.

Each LSR along the path MUST record the CLASSTYPE object, when it is
present, in its path state block.

If the CLASSTYPE object is not present in the Path message, the LSR
MUST associate the Class-Type 0 to the LSP.

The destination LSR responding to the Path message by sending a Resv
message MUST NOT include a CLASSTYPE object in the Resv message
(whether or not the Path message contained a CLASSTYPE object).

During establishment of an LSP corresponding to the Class-Type N, the
LSR MUST perform admission control over the bandwidth available for
that particular Class-Type.

An LSR that recognizes the CLASSTYPE object and that receives a Path
message that:

- contains the CLASSTYPE object, but

- does not contain a LABEL_REQUEST object or does not have a
session type of LSP_Tunnel_IPv4,

MUST send a PathErr towards the sender with the error code
"Diffserv-aware TE Error" and an error value of "Unexpected CLASSTYPE
object". These codes are defined in Section 6.5.

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An LSR receiving a Path message with the CLASSTYPE object that:

- recognizes the CLASSTYPE object, but

- does not support the particular Class-Type,

MUST send a PathErr towards the sender with the error code
"Diffserv-aware TE Error" and an error value of "Unsupported Class-
Type". These codes are defined in Section 6.5.

An LSR receiving a Path message with the CLASSTYPE object that:

- recognizes the CLASSTYPE object, but

- determines that the Class-Type value is not valid (ie,
Class-Type value 0),

MUST send a PathErr towards the sender with the error code
"Diffserv-aware TE Error" and an error value of "Invalid Class-Type
value". These codes are defined in Section 6.5.

An LSR receiving a Path message with the CLASSTYPE object, which:

- recognizes the CLASSTYPE object and

- supports the particular Class-Type, but

- determines that the tuple formed by (i) this Class-Type and
(ii) the setup priority signaled in the same Path message, is
not one of the eight TE-Classes configured in the TE-class
mapping,

MUST send a PathErr towards the sender with the error code
"Diffserv-aware TE Error" and an error value of "CT and setup
priority do not form a configured TE-Class". These codes are defined
in Section 6.5.

An LSR receiving a Path message with the CLASSTYPE object that:

- recognizes the CLASSTYPE object and

- supports the particular Class-Type, but

- determines that the tuple formed by (i) this Class-Type and
(ii) the holding priority signaled in the same Path message,
is not one of the eight TE-Classes configured in the TE-class
mapping,
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MUST send a PathErr towards the sender with the error code
"Diffserv-aware TE Error" and an error value of "CT and holding
priority do not form a configured TE-Class". These codes are defined
in Section 6.5.

An LSR receiving a Path message with the CLASSTYPE object that:

- recognizes the CLASSTYPE object and

- supports the particular Class-Type, but

- determines that the tuple formed by (i) this Class-Type and
(ii) the setup priority signaled in the same Path message, is
not one of the eight TE-Classes configured in the TE-class
mapping, AND

- determines that the tuple formed by (i) this Class-Type and
(ii) the holding priority signaled in the same Path message,
is not one of the eight TE-Classes configured in the TE-class
mapping

MUST send a PathErr towards the sender with the error code
"Diffserv-aware TE Error" and an error value of "CT and setup
priority do not form a configured TE-Class AND CT and holding
priority do not form a configured TE-Class". These codes are defined
in Section 6.5.

An LSR receiving a Path message with the CLASSTYPE object and with
the DIFFSERV object for an L-LSP that:

- recognizes the CLASSTYPE object,

- has local knowledge of the relationship between Class-Types
and Per Hop Behavior (PHB) Scheduling Class, eg, via
configuration, and

- determines, based on this local knowledge, that the PHB
Scheduling Class (PSC) signaled in the DIFFSERV object is
inconsistent with the Class-Type signaled in the CLASSTYPE
object,

MUST send a PathErr towards the sender with the error code
"Diffserv-aware TE Error" and an error value of "Inconsistency
between signaled PSC and signaled CT". These codes are defined below
in Section 6.5.
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An LSR receiving a Path message with the CLASSTYPE object and with
the DIFFSERV object for an E-LSP that:

- recognizes the CLASSTYPE object,

- has local knowledge of the relationship between Class-Types
and PHBs (e.g., via configuration)

- determines, based on this local knowledge, that the PHBs
signaled in the MAP entries of the DIFFSERV object are
inconsistent with the Class-Type signaled in the CLASSTYPE
object,

MUST send a PathErr towards the sender with the error code
"Diffserv-aware TE Error" and an error value of "Inconsistency
between signaled PHBs and signaled CT". These codes are defined in
Section 6.5.

An LSR MUST handle situations in which the LSP cannot be accepted for
reasons other than those already discussed in this section, in
accordance with [RSVP-TE] and [DIFF-MPLS] (eg, a reservation is
rejected by admission control, and a label cannot be associated).

6.4. Non-support of the CLASSTYPE Object

An LSR that does not recognize the CLASSTYPE object Class-Num MUST
behave in accordance with the procedures specified in [RSVP] for an
unknown Class-Num whose format is 0bbbbbbb (ie, it MUST send a
PathErr with the error code "Unknown object class" toward the
sender).

An LSR that recognizes the CLASSTYPE object Class-Num but that does
not recognize the CLASSTYPE object C-Type, MUST behave in accordance
with the procedures specified in [RSVP] for an unknown C-type (ie,
it MUST send a PathErr with the error code "Unknown object C-Type"
toward the sender).

Both of the above situations cause the path setup to fail. The
sender SHOULD notify the operator/management system that an LSP
cannot be established and might take action to retry reservation
establishment without the CLASSTYPE object.

6.5. Error Codes for Diffserv-aware TE

In the procedures described above, certain errors are reported as a
"Diffserv-aware TE Error". The value of the "Diffserv-aware TE
Error" error code is 28.
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The following table defines error values for the Diffserv-aware TE
Error:

Value Error

1 Unexpected CLASSTYPE object
2 Unsupported Class-Type
3 Invalid Class-Type value
4 Class-Type and setup priority do not form a configured
TE-Class
5 Class-Type and holding priority do not form a
configured TE-Class
6 Class-Type and setup priority do not form a configured
TE-Class AND Class-Type and holding priority do not form
a configured TE-Class
7 Inconsistency between signaled PSC and signaled
Class-Type
8 Inconsistency between signaled PHBs and signaled
Class-Type

See the IANA Considerations section for allocation of additional
values.

7. DS-TE Support with MPLS Extensions

There are a number of extensions to the initial base specification
for signaling [RSVP-TE] and IGP support for TE [OSPF-TE][ISIS-TE].
Those include enhancements for generalization ([GMPLS-SIG] and
[GMPLS-ROUTE]), as well as for additional functionality, such as LSP
hierarchy [HIERARCHY], link bundling [BUNDLE], and fast restoration
[REROUTE]. These specifications may reference how to encode
information associated with certain preemption priorities, how to
treat LSPs at different preemption priorities, or they may otherwise
specify encodings or behavior that have a different meaning for a
DS-TE router.

In order for an implementation to support both this specification for
Diffserv-aware TE and a given MPLS enhancement, such as those listed
above (but not limited to those), it MUST treat references to
"preemption priority" and to "Maximum Reservable Bandwidth" in a
generalized manner, ie, the manner in which this specification uses
those terms.

Additionally, current and future MPLS enhancements may include more
precise specification for how they interact with Diffserv-aware TE.
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7.1. DS-TE Support and References to Preemption Priority

When a router supports both Diffserv-aware TE and one of the MPLS
protocol extensions such as those mentioned above, encoding of values
of preemption priority in signaling or encoding of information
associated with preemption priorities in IGP defined for the MPLS
extension, MUST be considered an encoding of the same information for
the corresponding TE-Class. For instance, if an MPLS enhancement
specifies advertisement in IGP of a parameter for routing information
at preemption priority N, in a DS-TE environment it MUST actually be
interpreted as specifying advertisement of the same routing
information but for TE-Class [N]. On receipt, DS-TE routers MUST
also interpret it as such.

When there is discussion on how to comparatively treat LSPs of
different preemption priority, a DS-TE LSR MUST treat the preemption
priorities in this context as those associated with the TE-Classes of
the LSPs in question.

7.2. DS-TE Support and References to Maximum Reservable Bandwidth

When a router supports both Diffserv-aware TE and MPLS protocol
extensions such as those mentioned above, advertisements of Maximum
Reservable Bandwidth MUST be done with the generalized interpretation
defined in Section 4.1.1 as the aggregate bandwidth constraint across
all Class-Types. It MAY also allow the optional advertisement of all
BCs.

8. Constraint-Based Routing

Let us consider the case where a path needs to be computed for an LSP
whose Class-Type is configured to CTc and whose setup preemption
priority is configured to p.

Then the pair of CTc and p will map to one of the TE-Classes defined
in the TE-Class mapping. Let us refer to this TE-Class as TE-
Class[i].

The Constraint-Based Routing algorithm of a DS-TE LSR is still only
required to perform path computation satisfying a single BC which is
to fit in "Unreserved TE-Class [i]" as advertised by the IGP for
every link. Thus, no changes to the existing TE Constraint-Based
Routing algorithm itself are required.

The Constraint-Based Routing algorithm MAY also take into account,
when used, the optional additional information advertised in IGP such
as the BCs and the Maximum Reservable Bandwidth. For example, the
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BCs MIGHT be used as tie-breaker criteria in situations where
multiple paths, otherwise equally attractive, are possible.

9. Diffserv Scheduling

The Class-Type signaled at LSP establishment MAY optionally be used
by DS-TE LSRs to dynamically adjust the resources allocated to the
Class-Type by the Diffserv scheduler. In addition, the Diffserv
information (ie, the PSC) signaled by the TE-LSP signaling
protocols as specified in [DIFF-MPLS], if used, MAY optionally be
used by DS-TE LSRs to dynamically adjust the resources allocated by
the Diffserv scheduler to a PSC/OA within a CT.

10. Existing TE as a Particular Case of DS-TE

We observe that existing TE can be viewed as a particular case of
DS-TE where:

(i) a single Class-Type is used,
(ii) all 8 preemption priorities are allowed for that Class-Type,
and
(iii) the following TE-Class mapping is used:
TE-Class[i] <--> < CT0 , preemption i >
Where 0 <= i <= 7.

In that case, DS-TE behaves as existing TE.

As with existing TE, the IGP advertises:
- Unreserved Bandwidth for each of the 8 preemption priorities.

As with existing TE, the IGP may advertise:
- Maximum Reservable Bandwidth containing a BC applying across
all LSPs .

Because all LSPs transport traffic from CT0, RSVP-TE signaling is
done without explicit signaling of the Class-Type (which is only used
for Class-Types other than CT0, as explained in Section 6) as with
existing TE.

11. Computing "Unreserved TE-Class [i]" and Admission Control Rules

11.1. Computing "Unreserved TE-Class [i]"

We first observe that, for existing TE, details on admission control
algorithms for TE LSPs, and consequently details on formulas for
computing the unreserved bandwidth, are outside the scope of the
current IETF work. This is left for vendor differentiation. Note
that this does not compromise interoperability across various

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implementations because the TE schemes rely on LSRs to advertise
their local view of the world in terms of Unreserved Bw to other
LSRs. This way, regardless of the actual local admission control
algorithm used on one given LSR, Constraint-Based Routing on other
LSRs can rely on advertised information to determine whether an
additional LSP will be accepted or rejected by the given LSR. The
only requirement is that an LSR advertises unreserved bandwidth
values that are consistent with its specific local admission control
algorithm and take into account the holding preemption priority of
established LSPs.

In the context of DS-TE, again, details on admission control
algorithms are left for vendor differentiation, and formulas for
computing the unreserved bandwidth for TE-Class[i] are outside the
scope of this specification. However, DS-TE places the additional
requirement on the LSR that the unreserved bandwidth values
advertised MUST reflect all the BCs relevant to the CT associated
with TE-Class[i] in accordance with the Bandwidth Constraints Model.
Thus, formulas for computing "Unreserved TE-Class [i]" depend on the
Bandwidth Constraints Model in use and MUST reflect how BCs apply to
CTs. Example formulas for computing "Unreserved TE-Class [i]" Model
are provided for the Russian Dolls Model and Maximum Allocation Model
respectively in [DSTE-RDM] and [DSTE-MAM].

As with existing TE, DS-TE LSRs MUST consider the holding preemption
priority of established LSPs (as opposed to their setup preemption
priority) for the purpose of computing the unreserved bandwidth for
TE-Class [i].

11.2. Admission Control Rules

A DS-TE LSR MUST support the following admission control rule:

Regardless of how the admission control algorithm actually computes
the unreserved bandwidth for TE-Class[i] for one of its local links,
an LSP of bandwidth B, of setup preemption priority p and of Class-
Type CTc is admissible on that link if, and only if,:

B <= Unreserved Bandwidth for TE-Class[i]

where TE-Class [i] maps to < CTc , p > in the TE-Class mapping
configured on the LSR.

12. Security Considerations

This document does not introduce additional security threats beyond
those described for Diffserv ([DIFF-ARCH]) and MPLS Traffic
Engineering ([TE-REQ], [RSVP-TE], [OSPF-TE], [ISIS-TE]) and the same

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security measures and procedures described in these documents apply
here. For example, the approach for defense against theft- and
denial-of-service attacks discussed in [DIFF-ARCH], which consists of
the combination of traffic conditioning at DS boundary nodes along
with security and integrity of the network infrastructure within a
Diffserv domain, may be followed when DS-TE is in use. Also, as
stated in [TE-REQ], it is specifically important that manipulation of
administratively configurable parameters (such as those related to
DS-TE LSPs) be executed in a secure manner by authorized entities.

13. IANA Considerations

This document creates two new name spaces that are to be managed by
IANA. Also, a number of assignments from existing name spaces have
been made by IANA in this document. They are discussed below.

13.1. A New Name Space for Bandwidth Constraints Model Identifiers

This document defines in Section 5.1 a "Bandwidth Constraints Model
Id" field (name space) within the "Bandwidth Constraints" sub-TLV,
both for OSPF and ISIS. The new name space has been created by the
IANA and they will maintain this new name space. The field for this
namespace is 1 octet, and IANA guidelines for assignments for this
field are as follows:

o values in the range 0-239 are to be assigned according to the
"Specification Required" policy defined in [IANA-CONS].

o values in the range 240-255 are reserved for "Private Use" as
defined in [IANA-CONS].

13.2. A New Name Space for Error Values under the "Diffserv-aware TE
Error"

An Error Code is an 8-bit quantity defined in [RSVP] that appears in
an ERROR_SPEC object to define an error condition broadly. With each
Error Code there may be a 16-bit Error Value (which depends on the
Error Code) that further specifies the cause of the error.

This document defines in Section 6.5 a new RSVP error code, the
"Diffserv-aware TE Error" (see Section 13.3.4). The Error Values for
the "Diffserv-aware TE Error" constitute a new name space to be
managed by IANA.

This document defines, in Section 6.5, values 1 through 7 in that
name space (see Section 13.3.5).

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Future allocations of values in this name space are to be assigned by
IANA using the "Specification Required" policy defined in
[IANA-CONS].

13.3. Assignments Made in This Document

13.3.1. Bandwidth Constraints sub-TLV for OSPF Version 2

[OSPF-TE] creates a name space for the sub-TLV types within the "Link
TLV" of the Traffic Engineering Link State Advertisement (LSA) and
rules for management of this name space by IANA.

This document defines in Section 5.1 a new sub-TLV, the "Bandwidth
Constraints" sub-TLV, for the OSPF "Link" TLV. In accordance with
the IANA considerations provided in [OSPF-TE], a sub-TLV type in the
range 10 to 32767 was requested, and the value 17 has been assigned
by IANA for the "Bandwidth Constraints" sub-TLV.

13.3.2. Bandwidth Constraints sub-TLV for ISIS

[ISIS-TE] creates a name space for the sub-TLV types within the ISIS
"Extended IS Reachability" TLV and rules for management of this name
space by IANA.

This document defines in Section 5.1 a new sub-TLV, the "Bandwidth
Constraints" sub-TLV, for the ISIS "Extended IS Reachability" TLV.
In accordance with the IANA considerations provided in [ISIS-TE], a
sub-TLV type was requested, and the value 22 has been assigned by
IANA for the "Bandwidth Constraints" sub-TLV.

13.3.3. CLASSTYPE Object for RSVP

[RSVP] defines the Class Number name space for RSVP object, which is
managed by IANA. Currently allocated Class Numbers are listed at
http://www.iana.org/assignments/rsvp-parameters.

This document defines in Section 6.2.1 a new RSVP object, the
CLASSTYPE object. IANA has assigned a Class Number for this RSVP
object from the range defined in Section 3.10 of [RSVP] for objects
that, if not understood, cause the entire RSVP message to be rejected
with an error code of "Unknown Object Class". Such objects are
identified by a zero in the most significant bit of the class number
(i.e., Class-Num = 0bbbbbbb).

IANA assigned Class-Number 66 to the CLASSTYPE object. C_Type 1 is
defined in this document for the CLASSTYPE object.

[RSVP] defines the Error Code name space and rules for management of
this name space by IANA. Currently allocated Error Codes are listed
at http://www.iana.org/assignments/rsvp-parameters.

This document defines in Section 6.5 a new RSVP Error Code, the
"Diffserv-aware TE Error". In accordance with the IANA
considerations provided in [RSVP], Error Code 28 was assigned by IANA
to the "Diffserv-aware TE Error".

13.3.5. Error Values for "Diffserv-aware TE Error"

An Error Code is an 8-bit quantity defined in [RSVP] that appears in
an ERROR_SPEC object to define an error condition broadly. With each
Error Code there may be a 16-bit Error Value (which depends on the
Error Code) that further specifies the cause of the error.

This document defines in Section 6.5 a new RSVP error code, the
"Diffserv-aware TE Error" (see Section 13.3.4). The Error Values for
the "Diffserv-aware TE Error" constitute a new name space to be
managed by IANA.

This document defines, in Section 6.5, the following Error Values for
the "Diffserv-aware TE Error":

Value Error

1 Unexpected CLASSTYPE object
2 Unsupported Class-Type
3 Invalid Class-Type value
4 Class-Type and setup priority do not form a configured
TE-Class
5 Class-Type and holding priority do not form a configured
TE-Class
6 Class-Type and setup priority do not form a configured
TE-Class AND Class-Type and holding priority do not
form a configured TE-Class
7 Inconsistency between signaled PSC and signaled
Class-Type
8 Inconsistency between signaled PHBs and signaled
Class-Type

There are situations where a head-end needs to compute paths for
multiple LSPs over a short period of time. There are potential
advantages for the head-end in trying to predict the impact of the
n-th LSP on the unreserved bandwidth when computing the path for the
(n+1)-th LSP, before receiving updated IGP information. For example,
better load-distribution of the multiple LSPs would be performed
across multiple paths. Also, when the (n+1)-th LSP would no longer
fit on a link after establishment of the n-th LSP, the head-end would
avoid Connection Admission Control (CAC) rejection. Although there
are a number of conceivable scenarios where worse situations might
result, doing such predictions is more likely to improve situations.
As a matter of fact, a number of network administrators have elected
to use such predictions when deploying existing TE.

Such predictions are local matters, are optional, and are outside the
scope of this specification.

Where such predictions are not used, the optional BC sub-TLV and the
optional Maximum Reservable Bandwidth sub-TLV need not be advertised
in IGP for the purpose of path computation, since the information
contained in the Unreserved Bw sub-TLV is all that is required by
Head-Ends to perform Constraint-Based Routing.

Where such predictions are used on head-ends, the optional BCs sub-
TLV and the optional Maximum Reservable Bandwidth sub-TLV MAY be
advertised in IGP. This is in order for the head-ends to predict as
accurately as possible how an LSP affects unreserved bandwidth values
for subsequent LSPs.

Remembering that actual admission control algorithms are left for
vendor differentiation, we observe that predictions can only be
performed effectively when the head-end LSR predictions are based on
the same (or a very close) admission control algorithm as that used
by other LSRs.

Appendix B: Solution Evaluation

B.1. Satisfying Detailed Requirements

This DS-TE Solution addresses all the scenarios presented in
[DSTE-REQ].

It also satisfies all the detailed requirements presented in
[DSTE-REQ].

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The objective set out in the last paragraph of Section 4.7 of
[DSTE-REQ], "Overbooking", is only partially addressed by this DS-TE
solution. Through support of the "LSP size Overbooking" and "Link
Size Overbooking" methods, this DS-TE solution effectively allows CTs
to have different overbooking ratios and simultaneously allows
overbooking to be tweaked differently (collectively across all CTs)
on different links. But, in a general sense, it does not allow the
effective overbooking ratio of every CT to be tweaked differently in
different parts of the network independently of other CTs, while
maintaining accurate bandwidth accounting of how different CTs
mutually affect each other through shared BCs (such as the Maximum
Reservable Bandwidth).

B.2. Flexibility

This DS-TE solution supports 8 CTs. It is entirely flexible as to
how Traffic Trunks are grouped together into a CT.

B.3. Extendibility

A maximum of 8 CTs is considered more than comfortable by the authors
of this document. A maximum of 8 TE-Classes is considered sufficient
by the authors of this document. However, this solution could be
extended to support more CTs or more TE-Classes if deemed necessary
in the future; this would necessitate additional IGP extensions
beyond those specified in this document.

Although the prime objective of this solution is support of
Diffserv-aware Traffic Engineering, its mechanisms are not tightly
coupled with Diffserv. This makes the solution amenable, or more
easily extendable, for support of potential other future Traffic
Engineering applications.

B.4. Scalability

This DS-TE solution is expected to have a very small scalability
impact compared to that of existing TE.

From an IGP viewpoint, the amount of mandatory information to be
advertised is identical to that of existing TE. One additional sub-
TLV has been specified, but its use is optional, and it only contains
a limited amount of static information (at most 8 BCs).

We expect no noticeable impact on LSP Path computation because, as
with existing TE, this solution only requires Constrained Shortest
Path First (CSPF) to consider a single unreserved bandwidth value for
any given LSP.
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From a signaling viewpoint, we expect no significant impact due to
this solution because it only requires processing of one additional
item of information (the Class-Type) and does not significantly
increase the likelihood of CAC rejection. Note that DS-TE has some
inherent impact on LSP signaling in that it assumes that different
classes of traffic are split over different LSPs so that more LSPs
need to be signaled. However, this is due to the DS-TE concept
itself and not to the actual DS-TE solution discussed here.

B.5. Backward Compatibility/Migration

This solution is expected to allow smooth migration from existing TE
to DS-TE. This is because existing TE can be supported as a
particular configuration of DS-TE. This means that an "upgraded" LSR
with a DS-TE implementation can directly interwork with an "old" LSR
supporting existing TE only.

This solution is expected to allow smooth migration when the number
of CTs actually deployed is increased, as it only requires
configuration changes. However, these changes need to be performed
in a coordinated manner across the DS-TE domain.

Appendix C: Interoperability with Non-DS-TE Capable LSRs

This DSTE solution allows operations in a hybrid network where some
LSRs are DS-TE capable and some are not, as may occur during
migration phases. This appendix discusses the constraints and
operations in such hybrid networks.

We refer to the set of DS-TE-capable LSRs as the DS-TE domain. We
refer to the set of non-DS-TE-capable (but TE-capable) LSRs as the
TE-domain.

Hybrid operations require that the TE-Class mapping in the DS-TE
domain be configured so that:

- a TE-Class exists for CT0 for every preemption priority
actually used in the TE domain, and

- the index in the TE-class mapping for each of these TE-
Classes is equal to the preemption priority.

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For example, imagine the TE domain uses preemption 2 and 3. Then,
DS-TE can be deployed in the same network by including the following
TE-Classes in the TE-Class mapping:

Another way to look at this is to say that although the whole TE-
class mapping does not have to be consistent with the TE domain, the
subset of this TE-Class mapping applicable to CT0 effectively has to
be consistent with the TE domain.

Hybrid operations also require that:

- non-DS-TE-capable LSRs be configured to advertise the Maximum
Reservable Bandwidth, and

- DS-TE-capable LSRs be configured to advertise BCs (using the
Max Reservable Bandwidth sub-TLV as well as the BCs sub-TLV,
as specified in Section 5.1).

RFC 4124 Protocols for Diffserv-aware TE June 2005
Let us consider the following example to illustrate operations:

LSR0--------LSR1----------LSR2
Link01 Link12

where:
LSR0 is a non-DS-TE-capable LSR
LSR1 and LSR2 are DS-TE-capable LSRs

Let's assume again that preemptions 2 and 3 are used in the TE-domain
and that the following TE-Class mapping is configured on LSR1 and
LSR2:
i <---> CT preemption
====================================
0 CT1 0
1 CT1 1
2 CT0 2
3 CT0 3
rest unused

- understand that LSR0 is not DS-TE-capable because it
advertised a Max Reservable Bw sub-TLV and no Bandwidth
Constraints sub-TLV, and

- conclude that only CT0 LSPs can transit via LSR0 and that
only the values CT0/2 and CT0/3 are meaningful in the
Unreserved Bw sub-TLV. LSR1 may effectively behave as if the
six other values contained in the Unreserved Bw sub-TLV were
set to zero.

Le Faucheur Standards Track [Page 33]

RFC 4124 Protocols for Diffserv-aware TE June 2005
In IGP for Link01, LSR1 will advertise:

- Max Reservable Bw sub-TLV = <m10>

- Bandwidth Constraints sub-TLV = <BC Model ID, x0, x1>

- Unreserved Bw sub-TLV =
<CT1/0, CT1/1, CT0/2, CT0/3, 0, 0, 0, 0>

On receipt of such advertisement, LSR0 will:

- ignore the Bandwidth Constraints sub-TLV (unrecognized)

- correctly process CT0/2 and CT0/3 in the Unreserved Bw sub-
TLV and use these values for CTO LSP establishment

- incorrectly believe that the other values contained in the
Unreserved Bw sub-TLV relate to other preemption priorities
for CT0; but it will actually never use those since we assume
that only preemptions 2 and 3 are used in the TE domain.

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